Studies were conducted to evaluate preplant incorporated (PPI), preemergence (PRE), and postemergence (POE) herbicide treatments on yellow nutsedge control and on growth and yield of transplanted onions. Most effective yellow nutsedge control (≥80%) was achieved with metolachlor applied PPI plus PRE. Metolachlor and SAN 582H were more effective applied PPI than PRE. Bentazon alone applied POE adequately controlled yellow nutsedge only 1 of 2 yr. Highest onion yields and percent jumbo bulbs were produced when treatments included metolachlor applied PPI.